As public awareness has increased regarding the endangering effects of pathogens in liquids and sludge from wastewater treatment plants, pertinent environmental laws and regulations for the protection of human health have become more stringent. This is particularly true for sludge from wastewater plants to be deposited on agricultural land sites, where the nutrients contained in the sludge are utilized for crop growth. There is a movement towards the banning of Class B sludge (for a definition, see US EPA Code 40 CFR, Part 503) for land applications because of the dangers to human and animal health due to the pathogens contained in Class B sludge. Some counties in California, which receive Class B sludge, have passed legislation banning such land application of Class B sludge, effective Dec. 31, 2002. In order to continue land application in these counties, which is essential for biosolids management programs, Class B sludge must be upgraded to Class A biosolids by removing the existing pathogens. Accordingly, a new economical and efficient process to upgrade Class B sludge to Class A biosolids is needed.
The quantity of Class B sludge that could be converted to Class A biosolids is enormous. Therefore, facilities to inactivate pathogens and virus in sludge should be able to handle these large quantities. This requirement limits the number of technologies available.
Currently, known technologies are primarily based on thermal treatment of sludge, heat drying and heat treatment, sewage sludge treatment in a high pH—high temperature process (alkaline treatment), thermophilic digestion, beta ray and gamma ray irradiation, pasteurization, and composting. The situation in which many wastewater treatment facilities find themselves is illustrated using the Sanitary District for the City of Los Angeles (as an example).
The City of Los Angeles currently transports nearly half a million tons of Class B sludge to agricultural land in Kern County. This sludge contains on the average 45,000 MPN/gram fecal coliform, as well as other microorganisms and virus. Effective Dec. 31, 2002, a new Kern County ordinance will effectively ban the land application of Class B sludge and allow only Class A biosolids (which are free of coliform bacteria, salmonella, helminth ova and enteric virus) to be land applied. Accordingly, the City of Los Angeles' Hyperion Treatment Plant has been actively studying the means of producing Class A biosolids. The plant concluded that among the above listed processes, the thermophilic anaerobic digestion appears best suited for the up-grading of their Class B sludge. In a paper presented at the 16th annual Residuals and Biosolids Management Conference, sponsored by the Water Environment Federation, in Austin, Tex., plant workers stated that the themophilic digestion of sludge requires heating the sludge to 130° F. for 12 days in a first stage of treatment. The sludge is then pumped to two, second stage digesters for six more days for more digestion. The demand on heat energy, and treatment time, for sludge treatment is enormous and leads to high costs.
U.S. Pat. No. 5,385,673 discloses a method of treating wastewater biosolids by destruction of pathogens and indicator organisms to meet or exceed USEPA Process to Further Reduce Pathogens standards. The method first depresses the pH to below 5, followed by pH increase to 12 or higher, causing an exothermic reaction and heat of hydration. The mixture is placed within a confined volume to maintain the temperature at or above 55 degrees Celsius (° C.) for at least two hours. The mixture can be dewatered for a higher percent solid characteristic. The material is then tested and if test results indicate, the material is approved by the Environmental Protection Agency for human contact. The biosolid materials are suitable for general nutrient values with minimal regulatory restriction and other beneficial uses. U.S. Pat. No. 5,385,673 is herein incorporated by reference in its entirety.
U.S. Pat. No. 5,422,015 discloses a process to treat solid waste such as sewage sludge containing fecal matter to reduce pathogens by at least 90 percent and convert the waste to a useful product such as an amendment to agricultural land by combining the waste with an acid such as concentrated sulfuric and a base such as fly ash which exothermically react and thermally pasteurize the waste and add mineral value to the product. Pozzolanic materials, such as fly ash agglomerate the product and after grinding, the particles can aerate soil. The calcium oxide in fly ash reacts with sulfuric acid to form calcium sulfate dihydrate, a soil amendment. The amount of sulfuric acid can be controlled to provide a product with acid pH which is useful to neutralize alkaline soils such as those found in the Western United States of America. U.S. Pat. No. 5,422,015 is herein incorporated by reference in its entirety.
U.S. Pat. No. 5,853,450 discloses a method of treating wastewater or bio-organic sludges containing odor, animal viruses, pathogenic bacteria, and parasites to produce a bioactive but stabilized product that is useful as a soil substitute or as a fertilizer which can be applied directly to lands which consists essentially of the following steps: mixing said sludge with at least one alkaline material, wherein the amount of added material mixed with said sludge is sufficient to raise the pH of said mixture to pH 12, and raise the conductivity to disinfect and stabilize the sludge, and adding green waste at different process locations so that a biological action occurs converting the greenwaste into a soil-like granular product with improved odor over that of the treated municipal sludge alone or a composted greenwaste alone. U.S. Pat. No. 5,853,450 is herein incorporated by reference in its entirety.
U.S. Pat. No. 6,123,483 discloses a method of treating contaminated soil and mud that comprises mixing the solid and mud with water for washing in a wet-type mixing and grinding mill, separating less contaminated larger particles from more contaminated smaller particles, and exposing more contaminated smaller particles together with the eluate to mechano-chemically activated sorption media. U.S. Pat. No. 6,123,483 is herein incorporated by reference in its entirety.
Austrian Patent “AT PS No. 2002280” issued to O. Skoeldberg, dated Feb. 25, 1959, discloses an ultrasound system. The system uses pressure waves with intermittent impulses of high pressure amplitude to sterilize samples. Austrian Patent “AT PS No. 2002280” is herein incorporated by reference in its entirety.
German Patent Number DE 3903648 A (19900816) titled “VIRUS INACTIVATION IN LIQUIDS—BY GENERATING CAVITATION” discloses an installation for deactivating viruses in liquids that includes creating cavitation in the liquid using a high pressure pump and a homogenizing valve. The pump is a membrane pump and the valve pref. has a number of over flow edge sections. German Patent Number DE 3903648 A is herein incorporated by reference in its entirety.
Austrian Patent Number 389 889 B, dated Feb. 12, 1990 discloses the application of hypersonic sound for the inactivation of a virus in blood. Austrian Patent Number 389 889 B is herein incorporated by reference in its entirety.